Current driver circuit



March 8, 1966 F, BOND CURRENT DRIVER CIRCUIT Filed July 5, 1961 76 lllll72 BI 55 82 83 H FIG. 2 F

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I54 I43 I45 I34 '76 I44 I46 INVENTOR MILTON F. BOND ATTORNEY UnitedStates Patent 3,239,681 CURRENT DRIVER CIRCUIT Milton F. Bond,Apalachin, N.Y., assignor to International Business MachinesCorporation, New York, N.Y., a corporation of New York Filed July 3,1961, Ser. No. 121,412 3 Claims. (Cl. 307-88) This invention relatesgenerally to current driver circuits and more particularly to a constantcurrent pulse driver circuit for driving a variable impedance load.

A current driver circuit provides current for an impedance load. For avariable impedance load, it has heretofore been diflicult to maintain anappropriate current level over the entire range of the impedancevariation. In certain applications of magnetic cores, with substantiallyrectangular hysteresis loops, a plurality of the cores are in randomremanence states. Since in these applications both the magnitude of theinitial magnetic core load and time variation of the impedance thereofduring switching are often random, it has been difiicult to provide aconstant current pulse driver which would maintain the required constantcurrent level in the case load during the switching of the coresthereof.

It is an object of this invention to provide a current driver circuitfor an impedance load.

It is another object of this invention to provide a constant currentdriver circuit for a variable impedance load.

It is still another object of this invention to provide a constantcurrent pulse driver circuit for a variable impedance load over theentire range of the impedance variation.

It is a further object of this invention to provide a constant currentpulse driver circuit for a magnetic core load with unpredictable initialimpedance and time variation thereof.

It is still a further object of this invention to provide a constantcurrent pulse driver circuit for a magnetic core load which has acurrent pulse time duration required to switch every magnetic coretherein.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrattedin the accompanying drawings.

In the drawings:

FIGURE 1 illustrates a first preferred embodiment of this inventionhaving a feedback network connected between the emitter and base of adriver transistor which utilizes a control magnetic core and a Zenerdiode to assure a constant voltage pulse feedback during switching ofthe magnetic core load.

FIGURE 2 illustrates the substantially rectangular hysteresis loop forthe magnetic cores described for this invention.

FIGURE 3 illustrates a second preferred embodiment of this inventionwhich differs from the embodiment thereof shown in FIG. 1 in that thefeedback network includes, instead of the Zener diode, an RC network toprovide shaping for the feedback voltage pulse and a seriesresistor-diode path for controlling the switching time of the controlmagnetic core.

This invention provides a constant current pulse driver circuit for avariable impedance load whose initial impedance and impedance timevariation are random. It includes a current conductable switching devicewith current conduction control means therefor. The control means has afeedback circuit to assure that the application of a trigger signal tothe constant current pulse driver circuit causes constant currentconduction through the variable impedance load during the time variationof its impedance. The feedback circuit has a voltage pulse 3,239,681Patented Mar. 8, 1966 feedback magnitude limiting means and a netampereturns limiting means to assure that the action of the feedbackcircuit overlaps the time variation of the load impedance.

A feature of this invention involves a constant current pulse drivercircuit for resetting a magnetic core load having a plurality ofmagnetic cores with substantially rectangular hysteresis-loopcharacteristics. The collectoremitter current of a driver transistor inthe circuit is maintained constant by a feedback network which maintainsconstant the voltage across the base to emitter junction of thetransistor during the switching of the core load. The control winding ofa control magnetic core with a substantially rectangular hysteresis-loopcharacteristic is connected in series in the collector-emitter path. Thecollector-emitter current flows through the control winding and thewindings of the magnetic cores to be switched. A feedback winding on thecontrol core is connected between the emitter and base electrodes of thedriver transistor. Application of a positive going input trigger signalto the base of the driver transistor turns it 0N so thatcollector-emitter current flows to the magnetic core load. A voltage isinduced from the control winding on the control magnetic core to thefeedback winding thereon by transformer action which maintains a forwardbias on the base of the driver transistor. Therefore, the drivertransistor remains ON after the input trigger signal applied thereto hasterminated. The driver transistor turns OFF when the control magneticcore saturates. Saturation of the control magnetic core occurs becauseof its hysteresis-loop characteristic. When the control core saturates,the voltage across the feedback winding terminates and removes theforward bias on the base-emitter junction of the driver transistor.

A constant current pulse driver circuit in accordance with thisinvention has considerable utility, illustratively, for set and reset ofthe magnetic cores of magnetic core logic and memory circuits.

With reference to FIG. 1, the structure of a constant current pulsedriver 10, in accordance with this invention, for resetting a magneticcore load 12 will be described. The current driver 10 includes an NPNdriver transistor 14 having collector 16, base 18 and emitter 20. Inpractice, through conventional technique driver 10 can readily beadapted to incorporate a PNP driver transistor instead of the NPN drivertransistor 14. The collector 16 is connected to positive voltage source+V at terminal 22 via a resistor 24. Base 18 is connected toinputtrigger signal terminal 26 via diode 28 whose anode 30 is connected toinput trigger signal terminal 26 and whose cathode 32 is connected tobase 18. The emitter 20 is connected in series with control winding 34on control magnetic core 36. Control winding 34 passes through magneticcore load 12 in magnetic coupling relationship therewith by winding 37to ground 38. Magnetic core load 12 comprises, illustratively, magneticcores 40, 41, 42 and 43 in random initial remanence states. Magneticcore load 12 includes conventional windings on the magnetic coresthereof, not shown, for the practice of this invention, e.g., for alogic circuit, input and output windings, and for a memory circuit, setand sense windings. Feedback winding 44 on control magnetic core 36 iscon nected across Zener diode 46. Over a range of current, a Zener diodeprovides a constant voltage output. The anode 48 of Zener diode 46 isconnected to emitter 20 of driver transistor 14. Its cathode 50 isconnected via diode 52 to base 18 of driver transistor 14. Diode 52 hasits anode 54 connected to cathode 50 of Zener diode 46 and its cathode56 connected to base 18. Reset winding 58 on control magnetic core 36 isconnected to reset input terminal 60 and reset output terminal 62.

FIG. 2 presents an illustrative BH hysteresis curve 64 suitable forexplaining the remanence states of magnetic load cores 40 to 43 of coreload 12 and of control magnetic core 36. Hysteresis curve 64 hashorizontal axis H which measures the driving ampere turns applied to amagnetic core and vertical axis B which measures the magnetic inductionin the magnetic core. The hysteresis curve 64 is a substantiallyrectangular-loop with lower horizontal portion 66, right verticalportion 68, upper horizontal portion 70 and left vertical portion 7 2.Points 76 and 78 on hysteresis curve 64 indicate the 13 and B remanencestates, respectively, of an illustrative magnetic core. Illustratively,in logic and memory circuits points 76 and 78 may be termed the 1 andconditions. Points 80 and 82 on the H axis indicate the ampere-turnswhich are requisite for switching the illustrative magnetic core betweenB and B remanence states. In practice, points 80 and 82 are selected atapproximately twice the ampere-turns indicated by points 81 and 83,respectively. Usually, the positions of points 80 and 82 are selected asresult of power and switching time considerations.

The circuit operation of the current driver presented in FIG. 1 will nowbe described. A positive going voltage input trigger signal 84 isapplied to base 18 via input trigger signal terminal 26 and diode 28.The input trigger signal 84 causes transistor 14 to go from OFF to ONconduction. The collectonemitter current of transistor 14 flows throughcontrol winding 34 of control magnetic core 36 and the winding 37 ofcore load 12. The voltage which develops across control winding 34 iscoupled into feedback winding 44 by transformer action. Zener diode 4'6limits the magnitude of the voltage across feedback winding 44. Themagnitude of the limited voltage is the breakdown voltage of the Zenerdiode 46. The emitter voltage of driver transistor 14 rises as aconsequence of the voltage developed across core load 12 and controlwinding 34. However, since the feedback winding 44 is referenced to theemitter 20 voltage by being connected thereto and the voltage across thewinding is limited to a particular maximum voltage by the Zener diode46, a constant bias voltage equal to this maximum voltage is appliedacross the base 18 to emitter 20 junction. In practice, the Zener diodebreakdown characteristic is selected to assure that the particularmaximum voltage is always obtained. Therefore, a constant current pulse89 flows through control winding 34 and winding 37 to energize the coreload 12 until the control magnetic core 36 is switched from theremanence state 76 to point 31 on hysteresis curve 64. At point 91driver transistor 14 is no longer forward biased across its base-emitterjunction and its conduction terminates. Thereafter, the hysteresis curveof control magnetic core 36 returns to its remanence state 78. Duringthe switching of control magnetic core 36, all the magnetic cores ofcore load 12 not initially in the 0 condition are switched thereto fromthe 1 condition. It will be readily apparent to those skilled in the artthat diverse initial and final remanence states for core load 12magnetic cores 40 to 43 are obtainable through control of theirindividual ampere-turns.

Input diode 28 allows the input trigger signal 84 to be applied to base18 of driver transistor 14 and blocks the feedback voltage from feedbackwinding 44 from reaching input trigger signal terminal 26. In practice,if the feedback voltage is sufficient, diode 28 may be replaced by acapacitor. Feedback diode 52 prevents current flow from input triggersignal terminal 26 from flowing to feedback winding 44 duringapplication of input trigger signal 84 thereto. In practice, if triggersignal 84 is of sufficient magnitude, diode 52 may be removed fromconstant current pulse circuit 10. Zener diode 46 assures a constantvoltage across the base 18 to emitter 20 junction of driver transistor14 during switching of core load 12. Negative going reset signal 90applied to reset input and output terminals 60 and 62 resets controlmagnetic core 36 via reset winding 58. Alternatively, in practice, theresetting of control magnetic core 36 can be accomplished by a constantbias current in reset winding 58. The number of turns of feedbackwinding 44 on control magnetic core 36 is adjusted so that the netampere-turns on the control magnetic core 36 is less than the netampere-turns of the core load 12 during switching thereof. This assuresthat core load 12 will be completely switched when the switching actionof control magnetic core 36 terminates, i.e., the switching time ofcontrol magnetic core 36 is greater than the switching time of core load12.

FIG. 3 presents another preferred embodiment of a current driver inaccordance with this invention for resetting a magnetic core load. Theconstant current pulse driver 100 includes an NPN driver transistor 102with collector 104, base 106 and emitter 108. In practice the driver 100can readily be adapted to incorporate a PNP driver transistor instead ofNPN driver transistor 102 by those skilled in the electronics art.Collector 104 is connected via resistor 112 to positive voltage source+V terminal 110. Base 106 is connected to input trigger signal terminal114 via diode 116. Anode 118 of diode 116 is connected to input triggersignal terminal 114 and its cathode 120 is connected to base 106.Positive going input trigger signal 122 is applied to input triggersignal terminal 114. Emitter 108 of driver transistor 102 is connectedto control winding on control magnetic core 132 via diode 136. Diode 136has its anode 138 connected to emitter 108 and its cathode 140 connectedto control winding 130. Conductor 134 is wound on core load 142 and isconnected to ground 128.

Magnetic core load 142 includes illustrative magnetic cores 143 to 146with additional conventional windings thereon, not shown, for thepractice of this invention, e.g., for a logic circuit, input and outputwindings, and for a memory circuitry, set and sense windings. Cathode140 of diode 136 is connected to terminal 148 of feedback winding 150 oncontrol magnetic core 132. Terminal 152 of feedback control winding 150is connected to base 106 of driver transistor 102 via parallelarrangement of capacitor 154 and resistor 156 in series with diode 158.Diode 158 has its anode 160 connected to capacitor 154 and its cathode162 connected to base 106. The series path of resistor 164 and diode 166is connected between terminals 148 and 152 of feedback winding 150 oncontrol magnetic core 132. Diode 166 has its anode 168 connected toresistor 164 and its cathode 170 connected to terminal 148. Resetwinding 172 on control magnetic core 132 is connected to input resetterminal 174 and output reset terminal 176. Negative going reset signal178 is applied to reset input and output terminals 174 and 176.

The operation of the constant current pulse driver 100 presented by FIG.3 is as follows:

Input trigger voltage signal 122 applied to input trigger signalterminal 114 is passed via diode 116 to base 106 of driver transistor102 and causes collector-emitter current to flow therein. Thecollector-emitter current pulse 177 flows via diode 136 through controlwinding 130 on control magnetic core 132 and via conductor 134 throughcore load 142 to ground 128. The voltage developed across controlwinding 130 is coupled into feedback winding 150 by transformer action.The voltage at emitter 108 rises due to the voltage developed acrosscontrol winding 130 and core load 142. However, since feedback winding150 is referenced to emitter 108 via diode 136, the voltage acrossfeedback winding 150 maintains the base 106 to emitter 108 junction at asubstantially constant voltage until control magnetic core 132 isswitched. Illustratively, control magnetic core 132 switches from point76 to point 91 of the hysteresis curve 64 of FIG. 2. At point 91 drivertransistor 102 is no longer forward biased and collector 104 emittercurrent conduction ceases.

The parallel arrangement of capacitor 154 and resistor 156 is in seriesvia diode 158 with the input base resistance of driver transistor 102and forms therewith a voltage divider network which controls thefeedback voltage to the base 106. The charging of capacitor 154 causes amomentary voltage or current surge to base 106 and thereby improves therise time of driver transistor 102. In practice, the magnitude ofresistor 164 in parallel with feedback control winding 150 is controlledso that the net ampere-turns on control magnetic core 132 is such thatthe core load 142 completes its switching first. The magnitude ofresistor 164 is established at a value such that the net ampere-turns ofcontrol magnetic core 132 is less than that of core load 142. Diode 116prevents current flow at junction 163 from reaching input trigger signalterminal 114. In practice, if the feedback voltage is suificient diode116 may be replaced by a capacitor. Diode 166 in series with resistor164 prevents current flow in feedback win-ding 150 during resetting ofcontrol magnetic core 132. In practice, if the magnitude of resistor 164is sufliciently large, diode 166 is not required. Diode 136 increasesthe effective reverse breakdown voltage of the emitter 108 to base 106junction by acting as a voltage divider. In practice, where the normalreverse breakdown voltage of the emitter-base junction is not exceededduring circuit operation, diode 136 is not needed. Diode 158 in serieswith parallel arrangement of resistor 156 and capacitor 154 preventsflow of current into feedback winding 150 from input trigger signalterminal 114 during application of input trigger signal 12.2 thereto. Inpractice, if trigger signal 122 is of sufficient magnitude, diode 158may be removed from constant current pulse circuit 100. Application ofreset signal 178 to reset input and output terminals 174 and 176 resetscontrol magnetic core 132 via reset winding 172 thereon. Alternatively,in practice, the resetting of control magnetic core 132 can beaccomplished by a constant bias current in reset winding 172. It will beapparent to those skilled in the art that the triggering actiondescribed above can be obtained by utilizing an auxiliary winding on thecontrol magnetic core and applying thereto the input trigger signal.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. Constant current pulse driver for a variable impedance loadcomprising a current switching transistor having collector, base andemitter, said collector-emitter de fining a current path, a triggersignal input terminal connected via a first diode to said base, acontrol magnetic core with substantially rectangular hysteresis-loopcharacteristic, a control winding on said control core in series withsaid emitter-collector current path, a feedback winding on said controlmagnetic core, voltage reference means connected to said feedbackwinding and said collector-emitter current path for referencing saidbase and emitter at a controllable potential during said time variationof said variable impedance load, a second diode, said feedback windingbeing connected to said base via said second diode, said first andsecond diodes being poled so that said trigger signal is blocked fromapplying current to said feedback winding and said voltage developedacross said feedback winding is blocked from said input terminal, areset winding on said control core, reset signal means connected to saidreset winding adapted to cause reset current to flow therein therebyresetting said control core to its initial remanence state, said voltagereference means including a Zener diode connected across said feedbackwinding, said Zener diode being poled to reference the base and emitterto said Zener diode breakdown voltage.

2. Constant current pulse driver for a variable impedance loadcomprising a current switching transistor having collector, base andemitter, said collector-emitter defining a current path, a triggersignal input terminal connected via a first diode to said base, acontrol magnetic core with substantially rectangular hysteresis-loopcharacteristic, a control winding on said control core in series withsaid emitter-collector current path, a feedback winding on said controlmagnetic core, voltage reference means connected to said feedbackwinding and said collector-emitter current path for referencing saidbase and emitter at a controllable potential during said time variationof said variable impedance load, a second diode, said feedback windingbeing connected to said base via said second diode, said first andsecond diodes being poled so that said trigger signal is blocked fromapplying current to said feedback winding and said voltage developedacross said feedback winding is blocked from said input terminal, areset winding on said control core, reset signal means connected to saidreset winding adapted to cause reset current to flow therein therebyresetting said control core to its initial remanence state, said voltagereference including a Zener diode connected across said feedbackwinding, said Zener diode being poled to reference the base and emitterto said Zener diode breakdown voltage, and said variable impedance loadincluding a plurality of magnetic cores, each of said cores having asubstantially rectangular hysteresis loop and a random initial remanencestate and the time variation for switching each of said load magneticcores between its respective remanence states being variable.

3. A current driver for resetting a magnetic core load including incombination an input terminal, means for applying to said input terminalan input trigger signal, a diode, a driver transistor having acollector, a base and an emitter, said input terminal connected to saidvia said diode, said diode being connected in the forward directionbetween said input terminal and said base, a resistor, a source ofvoltage for said transistor, said collector being connected to saidvoltage source via said resistor, a core load including a plurality ofmagnetic cores therein, a control magnetic core, a control winding onsaid control core, a feedback winding on said control core, said controlwinding being magnetically coupled to said core load, a Zener diodeconnected across said feedback winding, said feedback winding beingconnected to said emitter to reference said base-emitter junction atsaid Zener diode breakdown potential, a second diode, said Zener diodebeing connected to said base via said second diode poled in the forwarddirection.

References Cited by the Examiner UNITED STATES PATENTS 2,920,213 1/1960Elias 307-88 2,997,600 8/1961 Hilberg et al. 307-88 3,134,023 5/1964Russell 307-88 3,140,400 7/1964 Shansky 30788 IRVING L. SRAGOW, PrimaryExaminer.

1. CONSTANT CURRENT PULSE DRIVER FOR A VARIABLE IMPEDANCE LOADCOMPRISING A CURRENT SWITCHING TRANSISTOR HAVING COLLECTOR, BASE ANDEMITTER, SAID COLLECTOR-EMITTER DEFINING A CURRENT PATH, A TRIGGERSIGNAL INPUT TERMINAL CONNECTED VIA A FIRST DIODE TO SAID BASE, ACONTROL MAGNETIC CORE WITH SUBSTANTIALLY RECTANGULAR HYSTERESIS-LOOPCHARACTERISTIC, A CONTROL WINDING ON SAID CONTROL CORE IN SERIES WITHSAID EMITTER-COLLECTOR CURRENT PATH, A FEEDBACK WINDING ON SAID CONTROLMAGNETIC CORE, VOLTAGE REFERENCE MEANS CONNECTED TO SAID FEEDBACKWINDING AND SAID COLLECTOR-EMITTER CURRENT PATH FOR REFERENCING SAIDBASE AND EMITTER AT A CONTROLLABLE POTENTIAL DURING SAID TIME VARIATIONOF SAID VARIABLE IMPEDANCE LOAD, A SECOND DIODE, SAID FEEDBACK WINDINGBEING CONNECTED TO SAID BASE VIA SAID SECOND DIODE, SAID FIRST ANDSECOND DIODES BEING POLED SO THAT SAID TRIGGER SIGNAL IS BLOCKED FROMAPPLYING CURRENT TO SAID FEEDBACK WINDING AND SAID VOLTAGE DEVELOPEDACROSS SAID FEEDBACK WINDING IS BLOCKED FROM SAID INPUT TERMINAL, ARESET WINDING ON SAID CONTROL CORE, RESET SIGNAL MEANS CONNECTED TO SAIDRESET WINDING ADAPTED TO CAUSE RESET CURRENT TO FLOW THEREIN THEREBYRESETTING SAID CONTROL CORE TO ITS INITIAL REMANENCE STATE, SAID VOLTAGEREFERENCE MEANS INCLUDING A ZENER DIODE CONNECTED ACROSS SAID FEEDBACKWINDING, SAID ZENER DIODE BEING POLED TO REFERENCE THE BASE AND EMITTERTO SAID ZENER DIODE BREAKDOWN VOLTAGE.